V/STOL aircraft are well known and commonly employ at least one gas turbine powerplant with one or more vectorable exhaust nozzle(s) which can be directed aft for forward propulsion in wing-borne flight and downwardly for jet-borne flight (hovering) and also in directions and conditions intermediate those mentioned.
One such aircraft has a centrally located powerplant with two fore and two aft vectorable or swivellable lift nozzles mounted directly on the powerplant so as to be symmetrically disposed about the centre of gravity of the aircraft. This has the advantage that the thrusts from the lift nozzles are readily balanced about the centre of gravity and the ducting to the lift nozzles can be made short and therefore efficient.
However, the central location of the powerplant in such aircraft is much further forward than in most other aircraft and imposes severe constraints on aircraft configuration, notably the centre fuselage/wing attachment structure and the undercarriage location and supporting structure. In addition, the forward location of the powerplant reduces the room for the air intake, which is compensated by providing sharp bends with consequent loss of efficiency. Likewise, the jet pipe of the powerplant leading to an outlet nozzle for providing thrust for horizontal flight is lengthened, which is a problem especially in an aircraft incorporating an afterburner for enhanced performance.
In a development of such aircraft, the gas turbine powerplant is located in the more conventional location towards the rear of the aircraft and one or more lift device(s) or nozzle(s) is or are located separately from the main body of the powerplant for supporting the aircraft during jet-borne flight. The supply to the lift devices is provided, on the one hand, by the main exhaust efflux from the powerplant and, on the other, by bleeding off cold low pressure air from the front of the powerplant and leading it through a pipe to a remote lift device. This arrangement is known as a remote lift system (RLS).
The advantage of such an arrangement is the greater freedom in locating the powerplant whilst still permitting thrust balance to be attained for jet-borne flight. However, the designs of RLS which are currently available all involve pipes situated externally of the main body or casing of the gas turbine powerplant for carrying air forward to the remotely situated lift device or devices; such an arrangement has drawbacks in various aspects of the aircraft design in terms of fuselage cross-section, airframe drag, fuel consumption and aircraft mass, at least.
It is also known in gas turbine powerplants to bleed off a small proportion of the low pressure compressor air through the compressor hub for the purposes of pressurizing seals and providing cooling for lubricant oil and turbine blades. Such air is utilised for assisting in compressor efficiency but has no utilisation for lift devices or nozzles.
It is an aim of the present invention to provide a gas turbine powerplant including a supply for one or more lift devices or nozzles which overcomes the various problems described above and combines efficient and effective lifting with a compact powerplant design.